Stage-geared gearbox for motor vehicles

ABSTRACT

A stage-geared gearbox for motor vehicles, includes an unsynchronized basic gearbox, at least one synchronized auxiliary gear and at least one control unit for controlling engagement and disengagement of the gears of the gearbox and also neutral position. In the gearbox, the control unit is arranged so as, when input signals indicating that neutral position is selected are received, to put the synchronized auxiliary gear in neutral position.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device for motor vehicles accordingto the preamble of patent claim 1 below, which device concerns astage-geared gearbox for transmitting driving power from the engine tothe driving axles and driving wheels of the vehicle.

STATE OF THE ART

Automatic gearboxes of the automated stage-geared gearbox type havebecome increasingly common in heavy-duty vehicles as microcomputertechnology has developed further and made it possible, with a controlcomputer and a number of actuators, for example servo motors, toprecision-regulate engine speed, engagement and disengagement of anautomated disk clutch between the engine and the gearbox and also thecoupling means of the gearbox in relation to one another, so that softshifting is always obtained at the correct engine speed. In heavy-dutyvehicles, these automatic gearboxes are often equipped with a basicgearbox, which has unsynchronized forward and reverse gears, and alsosynchronized auxiliary gears, which auxiliary gears can be arranged inseries before and/or after the basic gearbox. An example of an auxiliarygear arranged serially before the basic gearbox is a split gear and ofan auxiliary gear arranged serially after the basic gearbox is a rangegear (see, for example, SE516751). On shifting between theunsynchronized gears of the basic gearbox, such a selected gear issynchronized by the speed of the engine of the vehicle beingprecision-controlled to the correct speed before engagement of theselected gear takes place. The disk clutch is consequently engaged whensuch precision-control takes place.

The advantage of this type of automatic gearbox compared with aconventional automatic gearbox constructed with planetary gear stagesand with a hydrodynamic torque converter on the input side is on the onehand that, especially as far as use in heavy-duty vehicles is concerned,it is simpler and more robust and can be manufactured at a considerablylower cost than the conventional automatic gearbox and on the other handthat it has higher efficiency, which means lower fuel consumption ispossible.

According to the known art for the abovementioned type of automatedstage-geared gearbox, the following happens when neutral position isselected. When the transmission control system receives an input signalindicating that neutral position is selected, the unsynchronized basicgearbox is placed in its neutral position. This means that all the gearsof the basic gearbox are disengaged and consequently it is not possibleto transmit torque through the basic gearbox.

A disadvantage of this is that if it occurs while the vehicle is beingdriven, the gearbox can be rendered useless if the engine of the vehicleshould stop. If the engine cannot be controlled, a new gear in the basicgearbox cannot be selected, because the synchronization of a gear takesplace by means of precision-control of the speed of rotation of theengine. Consequently, a new gear in the basic gearbox cannot be engaged.The control system does not allow shifting because the gearbox may bedamaged. As the steering servo pump, for example, is usually driven bythe engine, units which are driven by the steering servo pump stopfunctioning, which means that the vehicle becomes sluggish to steer.Moreover, any engine brakes present cannot be engaged either for brakingthe vehicle.

There is consequently a need in a vehicle equipped with an automatedstage-geared gearbox, where the basic gearbox is unsynchronized and atleast one auxiliary gear is synchronized, to ensure that the gearbox isnot rendered useless when the vehicle is being driven, the gearbox is inneutral position and the engine stops.

SUMMARY OF THE INVENTION

The solution of the problem according to the invention as far as thedevice according to the invention is concerned is described in patentclaim 1. The other patent claims describe preferred embodiments anddevelopments of the device according to the invention (2 and 3).

The device according to the invention describes a stage-geared gearboxfor motor vehicles, comprising an unsynchronized basic gearbox, at leastone synchronized auxiliary gear and at least one control unit forcontrolling engagement and disengagement of the gears of the gearbox andalso neutral position. The gearbox is characterized in that the controlunit is arranged so as, when input signals indicating that neutralposition is selected are received, to put the synchronized auxiliarygear in neutral position.

The advantage of the device according to the invention is that it ispossible to engage a gear when the vehicle is being driven, the gearboxis in neutral position and the engine stops. As the auxiliary gear issynchronized, no external arrangements for synchronizing the speed ofrotation are required. The gearbox is consequently not rendered uselesson account of the engine having stopped.

In a first embodiment of the device according to the invention, thecontrol unit is arranged so as in the unsynchronized basic gearbox tokeep the previous selected gear engaged at the same time as asynchronized auxiliary gear is placed in its neutral position.

The advantage of the device according to the invention is that in thisway, together with the fact that the auxiliary gear is engaged either inlow gear position (LS) or high gear position (HS), a total gearingthrough the entire gearbox is obtained.

Further embodiments of the invention emerge from the subsequentdependent patent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in greater detail below withreference to the accompanying drawings, which, for the purpose ofexemplification, show further preferred embodiments of the invention andalso the technical background.

FIG. 1 shows a diagrammatic representation of an internal combustionengine with adjacent clutch and gearbox.

FIG. 2 shows the clutch and the gearbox in FIG. 1 on enlarged scale.

In FIG. 1, reference number 1 designates a six-cylinder internalcombustion engine, for example a diesel engine, the crankshaft 2 ofwhich is coupled to a single-plate dry disk clutch, designated generallyby reference number 3, which is enclosed in a clutch case 4. Thecrankshaft 2 is, via the output shaft 51 of the engine, connectednon-rotatably to the clutch housing 5 of the clutch 3, while its plate 6is connected non-rotatably to an input shaft 7 which is mountedrotatably in the casing 8 of a gearbox designated generally by referencenumber 9. A main shaft 10 and an intermediate shaft 11 are also mountedrotatably in the casing 8.

As can be seen most clearly from FIG. 2, a gearwheel 12 is mountedrotatably on the input shaft 7 and is lockable on the shaft by means ofa coupling sleeve 13 which is provided with synchronizing means and ismounted non-rotatably but axially displaceably on a hub 14 connectednon-rotatably to the input shaft 7. By means of the coupling sleeve 13,a gearwheel 15 mounted rotatably on the main shaft 10 is also lockablerelative to the input shaft 7. With the coupling sleeve 13 in a centralposition, both the gearwheels 12 and 15 are disengaged from their shafts7 and, respectively, 10. The gearwheels 12 and 15 engage with gearwheels16 and, respectively, 17 which are connected non-rotatably to theintermediate shaft 11. Arranged in a rotationally fixed manner on theintermediate shaft 11 are further gearwheels 18, 19 and 20 which engagewith gearwheels 21, 22 and, respectively, 23 which are mounted rotatablyon the main shaft 10 and are lockable on the main shaft by means ofcoupling sleeves 24 and, respectively, 25 which, in the illustrativeembodiment shown, do not have synchronizing devices. A further gearwheel28 is mounted rotatably on the main shaft 10 and engages with anintermediate gearwheel 30 which is mounted rotatably on a separate shaft29 and in turn engages with the intermediate shaft gearwheel 20. Thegearwheel 28 is lockable on its shaft by means of a coupling sleeve 26.

The gearwheel pairs 12, 16 and 15, 17 and the coupling sleeve 13 form asynchronized split gear with a low gear stage LS and a high gear stageHS. The gearwheel pair 15, 17 also forms, together with the gearwheelpairs 21, 18, 22, 19, 23, 20 and 28, 30, a basic gearbox with fourforward gears and one reverse gear. Arranged in a rotationally fixedmanner on the output end of the main shaft is a gearwheel 31 which formsthe sun gear in a two-stage synchronized range gear of planetary typewhich is designated by reference number 32 and the planet-wheel carrier33 of which is connected in a rotationally fixed manner to a shaft 34which forms the output shaft of the gearbox. The planet wheels 35 of therange gear 32 engage with a ring gear 36 which, by means of a couplingsleeve 37, is lockable relative to the gearbox casing 8 for low range LRand relative to the planet-wheel carrier 33 for high range HR.

The coupling sleeves 13, 24, 25, 26 and 37 are displaceable as shown bythe arrows in FIG. 2, the gear stages shown in conjunction with thearrows being obtained. The coupling sleeves 13, 24, 25 each have threepositions; two gear positions and a neutral position N (centralposition). The coupling sleeve 26 has one gear position and a neutralposition N. The coupling sleeve 37 has two gear positions LR and HR. Thedisplacement of the coupling sleeves is brought about by respectiveservo devices 40, 41, 42, 43 and 44 indicated diagrammatically in FIG.2, which can be pneumatically operated piston/cylinder arrangements ofthe type used in a gearbox of the type described above which is marketedunder the name I-shift.

The servo devices 40, 41, 42, 43 and 44 are controlled by an electroniccontrol unit 45 (see FIG. 1), comprising a microcomputer, depending onsignals fed into the control unit representing various engine andvehicle data comprising at least engine speed, vehicle speed, throttlepedal position and, where appropriate, engine brake on/off, when anelectronic gear selector 46 coupled to the control unit 45 is in itsautomatic shifting position. When the selector is in the position formanual shifting, shifting takes place at the command of the driver viathe gear selector 46.

The control unit 45 also controls the fuel injection via the enginecontrol unit 50.

When shifting of the unsynchronized gears in the basic gearbox takesplace, the speed is synchronized by precision-control of the speed ofrotation of the engine 1. Consequently, the disk clutch 3 is engaged, sothat the speed of rotation of the input shaft 7 and the intermediateshaft 11 is adapted to a new selected gearing. The engine speed isregulated depending on injected fuel quantity and engine brake.

When shifting of the synchronized gears, that is to say the split gearor range gear, takes place, the speed adaptation is effected bysynchronizing rings (not shown in figure). When such shifting takesplace, the disk clutch 3 is disengaged. The control unit 45 controls thefuel injection, that is to say the engine speed, depending on thethrottle pedal position and also the air supply to a pneumaticpiston/cylinder arrangement 47, by means of which the disk clutch 3 isdisengaged or engaged before and after engagement of a new selected gearis completed.

According to the invention, the control unit 45 is programmed so that,when the control unit 45 receives an input signal indicating thatneutral position is desired, the split gear 12, 13, 15, 16, 17 is put inits neutral position N. The input signal for neutral position can beobtained either by, when shifting is effected manually, the driverselecting neutral position via the gear selector 46 or by, when the gearselector 46 is located in its automatic position, the control system 45opting to shift to neutral position on the basis of certain given inputsignals, for example when the vehicle is in a state for freewheeling(see, for example, SE516751) and the vehicle is equipped with thisfunction.

If for any reason the engine 1 stops during driving and the gearbox 9 isat the same time in the neutral position, the control unit 45 is,according to the invention, programmed to engage either the low gearstage LS or the high gear stage HS of the split gear depending on thespeed of the vehicle. As the neutral position is obtained via asynchronized gear, synchronization can take place irrespective ofwhether the engine has stopped or not. The total gearing is obtainedtogether with the previous engaged gear in the basic gearbox, whichconsequently remains engaged while the neutral position is occupied aswell.

During normal driving, that is to say the engine does not stop while theneutral position is occupied, the control unit 45 opts to engage aselected gear, that is to say all the gears of the gearbox are availablefor shifting.

According to a special embodiment, when the vehicle is standing still,the unsynchronized basic gearbox can be placed in its neutral positionwhen neutral shifting is requested by means of, for example, the gearselector 46, as in such a stationary state the engine does not need tobe used for synchronizing the input shaft 7 and intermediate shaft 11 ofthe gearbox for a selected gearing. (This is normally effected by meansof what is known as an intermediate shaft brake which is not shown inthe figures.)

The functioning according to the invention can be obtained in acorresponding way with a range gear equipped with a neutral position.

1. A stage-geared gearbox for motor vehicles, comprising anunsynchronized basic gearbox, at least one synchronized auxiliary gearand at least one control unit for controlling engagement anddisengagement of the gears of the gearbox and also neutral position,wherein the control unit is arranged so as, when input signalsindicating that neutral position is selected are received, to put the atleast one synchronized auxiliary gear in neutral position.
 2. Thestage-geared gearbox as claimed in claim 1, wherein the control unit isarranged so as in the basic gearbox to keep a previous selected gearengaged while the neutral position is occupied.
 3. The stage-gearedgearbox as claimed in claim 2, wherein the auxiliary gear comprises asplit gear.
 4. The stage-geared gearbox as claimed in claim 2, whereinthe auxiliary gear comprises a range gear.
 5. The stage-geared gearboxas claimed in claim 1, wherein the auxiliary gear comprises a splitgear.
 6. The stage-geared gearbox as claimed in claim 1, wherein theauxiliary gear comprises a range gear.